The present invention relates to a reed switch glass tube and a method for manufacturing the same.
A reed switch comprises a contact point composed of opposed magnetic wire rods, and a glass tube for encapsulating the magnetic wire rods, which opens and closes the contact point by providing a magnetic field from the outside of the glass tube. Encapsulation of the magnetic wire rods into the glass tube is performed by inserting the magnetic wire rods into the glass tube under inert gas, reducing gas or under vacuum and softening by heating both end parts of the glass tube to be sealed.
When end parts of the reed switch glass tube have sharp corners and fine cracks, there are problems that the end parts of the glass tube are chipped and cracked typically during transport and shards thereof are mixed into the glass tube at the time of an encapsulation process. Therefore, glazing treatment to carry out rounding processing by heating the end parts of the glass tube with a burner to be softened has been conventionally performed.
However, in recent years, as an electron device has been downsized and light-weighted, a reed switch glass tube has been more and more decreased in diameter, thickness, and length. Typically, a minute reed switch glass tube having an outer diameter of 1.3 mm, a thickness of 0.2 mm, and a length of 3.1 mm had a problem that it was not possible to prevent, for example, chipping and cracking of end parts of the glass tube at the time of rounding processing by burner heating.
Until now, a technique for rounding end parts of the glass plate by the irradiation of laser light to a side of the glass plate is known (for example, Japanese Unexamined Patent Application Publication Nos.
The present invention has been made in view of the aforementioned problem with the conventional reed switch glass tube. It is an object of the present invention to provide a reed switch glass tube capable of reliably preventing, for example, chipping and cracking of end parts thereof typically during transport.
According to the present invention, there is provided a reed switch glass tube according to claim 1, which comprises a compressive stress layer formed at an end part of the glass tube, the compressive stress layer being formed on an outer circumference surface of the glass tube in the end part and having a length of 0.1 mm to 0.6 mm in a longitudinal direction.
In a preferred embodiment of the reed switch glass tube according to the present invention, stress in a compressive stress layer formed on an end face of the glass tube in the end part is greater than stress in the compressive stress layer formed on the outer circumference surface.
In another preferred embodiment of the reed switch glass tube according to the present invention, an infrared transmittance of glass of the reed switch glass tube at a wavelength of 1,050 nm is 10% or lower for a thickness of the glass of 0.5 mm.
According to the present invention, a method according to claim 4 is provided for manufacturing the reed switch glass tube of claim 1.
According to the reed switch glass tube of the present invention, a compressive stress layer having a length from an end face within the range of 0.1 mm to 0.6 mm is formed on an outer circumference surface of an end part of the glass tube. Accordingly, it is possible to reliably prevent the end parts of the glass tube from chipping and cracking or the like, even when contacting the outside typically during transport.
As shown in
Further, a length A in a longitudinal direction of the glass tube in the compressive stress layer 22 formed on the outer circumference surface 12 is set at about 0.4 mm. The Length A of the compressive stress layer 22 is preferably 0.1 mm to 0.6 mm. When the length A is smaller than 0.1 mm, it is impossible to effectively prevent, for example, chipping of end parts of the glass tube 10 caused by contact with the outside or the like. On the other hand, when the length A is greater than 0.6 mm, tensile stress which acts around the compressive stress layer 22 becomes greater as reaction of compressive stress in the compressive stress layer 22. As a result, this easily causes destruction of the glass tube 10, which is not preferable.
Furthermore, the reed switch glass tube 10 being an embodiment of the present invention is so formed that stress in the compressive stress layer 21 formed on the end face 11 is greater than stress in the compressive stress layer 22 formed on the outer circumference surface 12. This makes it possible to effectively prevent chipping of particularly the end face 11 out of the end parts 1 of the reed switch glass tube 10.
Moreover, the reed switch glass tube 10 being an embodiment of the present invention is formed of high-infrared absorption glass whose infrared transmittance at a wavelength of 1,050 nm is 10% or lower for a thickness of glass of the glass tube of 0.5 mm. This makes it possible to effectively absorb infrared rays of a halogen lamp at the time of encapsulation process of the reed switch. As a result, even when the glass tube is a minute glass tube, it is possible to securely seal both end parts thereof. When the glass tube has an infrared transmittance at a wavelength of 1,050 nm of over 10% for a thickness of the glass of 0.5 mm, infrared absorption from the halogen lamp becomes insufficient. As a result, not only extra time and energy are needed for the encapsulation process but also the amount of infrared rays that reaches inside the reed switch after transmitting the glass and a contact point portion of the reed switch is heated, resulting in arising of a problem of deterioration of magnetic property thereof.
As high-infrared absorption glass with an infrared transmittance at a wavelength of 1,050 nm of 10% or lower for a thickness of the glass of 0.5 mm, infrared absorption glass with a composition of 60% to 75% of SiO2, 1% to 10% of Al2O3, 0% to 10% of B2O3, 3. 5% to 10% of RO (R is one or more kinds selected from Ca, Mg, Ba, Sr or Zn), 0.5% to 5% of Li2O, 8% to 17% of Na2O+K2O, 2% to 10% of Fe3O4 in a weight percentage is preferably used.
While SiO2 is a major component necessary to constitute a glass skeleton, solubility is deteriorated as well as lowering of a linear thermal expansion coefficient when the content of SiO2 is more than 75% and chemical durability is deteriorated when the content of Sio2 is less than 60%. Accordingly, glass is transformed by chemical treatment such as electroplating in a reed switch manufacturing process. This makes it impossible to obtain weather resistance to maintain long-term reliability as electronic parts.
Although Al2O3 has remarkable effects for improving weather resistance of glass and controlling devitrification in glass dissolution, when the content of Al2O3 is more than 10%, dissolution of glass is difficult. When the content of Al2O3 is less than 1%, it is impossible to obtain the aforementioned effects.
B2O3 has the effect of increasing an efficiency of encapsulation by decreasing viscosity of glass along with promoting the dissolution of glass. However, when the content of B2O3 is more than 10%, chemical durability is deteriorated and it is impossible to obtain homogeneous glass due to an increase in evaporation at the time of dissolution.
CaO, MgO, BaO, SrO, and ZnO represented by RO have an improving effect on weather durability of glass as well as decreasing viscosity of glass. However, when the total content of RO is more than 10%, devitrification of glass is increased, resulting in difficulty in manufacturing homogeneous glass. When the content of RO is less than 3.5%, it is impossible to obtain the aforementioned effect.
Li2O has the effect of increasing a linear thermal expansion coefficient of the reed switch while keeping specific volume resistivity of glass which is needed as electric insulation of the reed switch high to some extent. Further, Li2O has a significantly profound effect as a flux and an effect of reducing viscosity, so that it is possible to minimize the content of B2O3 which is also a component that is easily evaporated while generally used as a flux of glass by using Li2O as an essential component. However, when the content of B2O3 contained in glass is more than 5%, weather resistance and devitrification of glass are deteriorated, which is not preferable. On the other hand, when glass has a content of B2O3 of less than 0.5%, it is impossible to obtain the aforementioned effect.
As is the case with Li2O, as well as increasing the linear thermal expansion coefficient of glass, Na2O and K2O are components to promote melting glass. However, when a total content of Na2O and K2O is over 17%, as well as excessively increasing the linear thermal expansion coefficient, weather resistance and specific volume resistivity of glass are significantly deteriorated. On the other hand, when the total content of Na2O and k2O is less than 8%, it is impossible to obtain a predetermined linear thermal expansion coefficient, resulting in difficulty in melting of glass.
In the case where the content of one component out of Li2O, Na2O, and K2O is restricted within 80% of the total amount alone, it is possible to obtain more superior weather resistance and high specific volume resistivity by operation of a mixed alkali effect.
Fe3O4 (Although FeO absorbs infrared rays, FeO coexists with Fe2O3 depending on redox in glass. All ferric oxide is represented by the conversion into Fe3O4.) is used as an essential component for allowing glass to have infrared absorption capacity. However, in the case where the content of Fe2O3 is more than 10%, vitrification becomes difficult and in the case where the content of Fe2O3 is less than 2%, it is impossible to restrict the infrared transmittance at a wavelength of 1,050 nm to 10% or lower for a thickness of the glass of 0.5 mm.
In addition, in the aforementioned glass, it is possible to add each component up to 3%, such as ZrO2 and Tio2 or the like for the purpose of adjusting viscosity of glass and improving devitrification and weather resistance.
Next, a method for manufacturing a reed switch glass tube 10 of the present invention is described as below.
First, a batch having the aforementioned composition is prepared and is then dissolved. Thus obtained melt glass is formed in the form of a tube to obtain an infrared absorption glass tube 3 by cutting to a predetermined length.
As shown in
This makes it possible to uniformly soften by heating the entire end face of each glass tube 3. It is possible to reliably form a compressive stress layer at the end parts thereof, even in the case of a minute reed switch glass tube. Further, it is possible to effectively absorb the laser light L irradiated to the end face of the infrared absorption glass tube 3 and in addition to that, it is possible to effectively soften by heating only around the surface of the end face. As a result, it is possible to suitably form a compressive stress layer having a stress greater than that of the compressive stress layer of the outer circumference surface on the end face of the glass tube 3.
Furthermore, a compressive stress layer is formed on an end part of each glass tube 3 by cooling by blowing air or naturally cooling the end face of each glass tube 3 soften by heating. In such a manner, the reed switch glass tube 10 of the present invention is produced.
As mentioned above, in the reed switch glass tube 10 of the present invention, the compressive stress layer 22 having a length A within a range of 0.1 mm to 0.6 mm from the end face 11 is formed on the outer circumference surface 12 of the end part 1 thereof. Accordingly, it is possible to reliably prevent, for example, chipping and cracking of the end parts of the glass tube even when making contact with the outside typically during transport.
In addition, the reed switch glass 10 can reliably prevent particularly chipping and cracking of the end face 11 thereof because the compressive stress layer 21 with a stress greater than a stress in the compressive stress layer 22 formed on the outer circumference surface 12 is formed on the end face 11 thereof.
Since glass of the reed switch glass tube 10 being an embodiment of the present invention has an infrared transmittance at a wavelength of 1,050 nm of 10% or lower for a thickness of the glass of 0.5 mm, it becomes possible to effectively absorb infrared rays of a halogen lamp at the time of an encapsulation process of the reed switch. As a result, even in the case of a minute glass tube, it is possible to securely seal both end parts of the glass tube.
While the reed switch glass tube 10 of the present invention has thus been described so far, the present invention may be embodied in other forms.
In the aforementioned embodiments, while a minute reed switch glass tube with an outer diameter of 1.75 mm, a thickness of 0.25 mm, and a length of 7.7 mm has been described so far as one example of a reed switch glass tube, it is to be understood that the present invention is not limited to this size and typically, a reed switch glass tube with an outer diameter of 4.95 mm, a thickness of 0.65 mm, and a length of 18.4 mm may be used.
10: reed switch glass tube; 1: end part; 11: end face; 12: outer circumference surface; 13: inner circumference surface; 2, 21, 22, 23: compressive stress layer; A: length of compressive stress layer on the outer circumference surface
This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.